Device for cleaning xerographic cylinders

ABSTRACT

A device for wiping clean xerographic cylinders using a web of cloth-like material maintained in contact with the drum as it rotates. The contact area covers a considerable angular extent of the drum for substantially its entire width and when compared to similar prior art devices, provides greater cleaning action, uses less web material per drum revolution, and reduces drum wear due to web contact.

United I States Patent n 1 J ovanovic DEVICE FOR CLEANING oXEROGRAPI-IIC CYLINDERS [76] Inventor: Dragan Jovanovic, l-lerzogstrasse521 U.S.Cl ..'.I .355/15, 15/15 51 Int. Cl. ..G03g 15/22 53 FieldofSearch ..3ss/3, 151; l5/1.5,256.52

[56] References Cited UNITED STATES PATENTS 3,186,838 6/1965 Graffet a1...355I15 X 3,099,856 8/1963 'Eichorn et al. "1355/15 X 3,526,457 9/1970Dirnond et a1 ..355/15 1 Jan. 23, 1973 FOREIGN PATENTS OR APPLICATIONS1,572,331 1/1970 Germany ..355/15 Primary Examiner-Samuel S. MatthewsAssistant Examiner -Fred L. Braun Attorney-Jacque L. Meister [57]ABSTRACT A device for wiping clean xerographic cylinders using a web ofcloth-like material maintained in contact with the drum as it rotates.The contact area covers a considerable angular extent of the drum forsubstantially its entire width and when compared to similar prior artdevices, provides greater cleaning action, uses less web material perdrum revolution, and reduces drum wear due to web contact.

3 Claims, 1 Drawing Figure PATENTfnJrmzs lsn EXPOSE TRANSFER DragonJovcmovic INVENTOR.

may

BY I ATTY BACKGROUND OF THE INVENTION The field of the invention isgenerally related to xerography and more particularly to improvements inthe method of cleaning the xerographic drum after the transfer of thedeveloped image to a paper copy.

In the branch of electrophotography commonly known as xerography, anelectrostatic image is formed by first charging and then exposing aphotoconductive insulatingsurface to a light pattern. The electrostaticimage is converted to a visible image by a development step wherein finecolored particles, called toners, are caused to adhere to theelectrostatic image on the photoconducting insulating surface. Thedeveloped image is then transferred to a paper carrier and fixed and theentire process is ready for repetition, except for one problem.Unfortunately, when the developed image is transferred to the papercarrier, the transfer is not absolutely complete. Some of the tonerparticles are left adhering to the photoconducting insulating surfaceafter the transfer, and must be removed if they are not to reduce thecontrast of subsequent copies. It is with respect to this cleaning cyclethat the invention is directed.

In many if not most of the modern xerographic copying machines, thephotoconducting insulating surface is a plate arranged into cylindricalform. In the majority of such machines continuous cleaning isaccomplished by one or more rotating fur-like brushes in contact withthe rotating drum. Supplemental vacuuming action often aids cleaning inthis type of device. However, the fur is relatively expensive and has arelatively short working life; 40-60 hours of operation being a typicallife. Since this life is relatively limited and other expensivecomponents are needed such as the vacuuming system, it would bedesirable to clean the drum in a manner that is less expensive toimplement and with a longer service life. One such device that is lessexpensive is the Web Cleaner Apparatus described in the U.S. Pat. No.3,099,856 of Eichorn et al. However, even though Eichorns device is lesscostly to implement than the prior art cleaning system, it, like itspredecessors, suffered from a shorter working life than desired.

BRIEF SUMMARY OF THE INVENTION It is accordingly a principal object ofthe invention to provide an improved device for cleaning xerographicdrums.

Yet another object of the invention is to provide a xerographic drumcleaning device having improved service life over that of prior artdevices.

Still another object of the invention is to provide a BRIEF DESCRIPTIONOF THE DRAWING The drawing illustrates in schematic form the functionalprocessingareas disposed about a xerographic drum and the inventivecleaning device in respect thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENT The various processing stationsemployed in xerography are shown in the drawing disposed about thecircumference of a xerographic drum 10 arranged to rotate about axis 16in the direction of arrow 17. The angular extent of each station isapproximately correct for most xerographic processing machines but thoseshown are exemplary only, the purpose being to show the relativelocation of the cleaning area and device in the station sequence. Asshown, the cleaning station occupies that area between the transfer andcharge area segments. As there shown, the cleaning sector has an angularextent of approximately 120. This is approximately the maximum areaavailable and is only achieved with relatively large diameter cylinderor drums on the order of l4l6 inches in diameter. Since the hardwarespace requirements to implement each station do not decrease appreciablyfor smaller drums, as drum size is made smaller, the space for thecleaning station decreases. For a cylinder/drum diameter of 7-9 inches,the cleaning station is typically limited to a -l05 sector. It is afeature of the invention that almost all of this sector is used for thecleaning station and, as a result of the novel arrangement and featuresof the cleaning device, the xerographic drum is cleaned more effectivelythan heretofore possible.

As shown, a web 18 of cleaning material is maintained in contact withthe drum over a large angular sector of the drum surface. The web 18 isfed from supply roll I4 in the direction of arrow 19 until it contactsthe drum at 39. Thence, it is conducted across the surface of the drumin a direction of arrow 20 to line 21 where it contacts pressure-roller13. From pressure roller 13, the web 18 is fed in the direction of arrow22 to takeup roller 15. Roller 15 is coupled to drum 10 by means of agear train (not shown). The gear train is selected to drive take uproller 15 at a rate in the range of H50 to H that of drum 10, theparticular speed depending on several factors as discussed furtherbelow.

In all embodiments of the cleaning device, the principal'web drive isthrough take up roller 15. Generally I find that no power should beapplied to pressure roller 13 and that supply roll 14 should either havea friction brake about its axle 27 or, that a garter spring drive fromtakeup roller 15 under driving supply roll 14 can be used to causebraking action. The axle 27 for supply roll 14 is mounted on swingingarm 23 which in turn rotates about pivot 24. The supply roll is lightlyspring biased against drum 10. In practice, the amount of this bias ismade as small as possible consistent with maintaining contact of the webwith drum when the system is not operating. Advantageously, the springbias is provided by an over-center spring arrangement, the spring 28connected between a spring stud 29 and swinging arm 23. With thisarrangement, I have found that maintaining a force of the supply rollagainst the drum of between 4-8 ounces generally is satisfactory.

Pressure roller 13 is mounted for rotation about axle 30 which, in turnis secured to swinging arm 25. Arm 25 rotates about pivot 26. Thepressure of roller 13 against the drum is considerably higher than thatof the supply roll since the pulling action of the web tends to pull thepressure roller away from the drum. This pressure is maintained bysprings (not shown) connected to arm 25. The springs are chosen tomaintain a pressure of V2 to 1 /2 pounds per lineal inch of feed rolllength while the drum and web are moving relative to each other. Thispressure is considerably less than that used in other web type cleaningdevices and, as a consequence, results in reduced wear on thexerographic drum. Nevertheless, even though there is less pressure, thecleaning action is superior by virtue of the large angular contactsector used in the inventive device compared to the substantially linecontact of prior art web type cleaning devices.

As pointed out above, various embodiments of the invention can havevariations in the angular sector of the xerographic drum wiped by thecleaning web, available space varying between about 75 and 120. The areaused for wiping contact is chosen based upon several variables includingrelative speed between the drum and cleaning web, the type of materialemployed in the web and, the amount ofinterstitial space between fibersof the web; the last factor apparently being of the greatest importance.While conventional cotton cloth, cheese cloth, asbestos cloth and clothscomprised of various artificial fibers have been utilized, the preferredweb material is a non-woven cellulose having between 15 and percent openspaces and approximately 7-9 mils thick. With such a material and thespeed of the web relative to the drum set between H75 and l/l00, thepreferred wiping area for a 9 inch diameter drum is a 75 sector or anarea 6% inches wide by drum length. With these parameters, very high webcollection efficiencies are achieved; about 96 percent of the availableinterstitial space of the web being filled with toner particles asrevealed by microscopic inspection. Further, since there is interstitialspace remaining in the web when it ceases contact with the drum, thereis a reduction in wear of the drum compared to systems where there isinsufficient interstitial space and hence, loose toner particles aretumbled between the advancing web and the drum, abrading the drum.

Other web materials yield slightly different optimum results. Ingeneral, the softer the web material the greater the collectionefficiency of the web. However, there is an optimum point on softness,reached when the pressure of the web against the drum in itself compactsthe web and thus tends to seal-off the interstitial spaces. In thedrawing, the various parts of the inventive apparatus are shownschematically in orthographic projection only. As will be obvious, thevarious cylinders and rolls in actual practice are supported betweenmain frames that have been omitted from the drawing for simplicity.

The invention has been described in detail herein with particularreference to preferred embodiments thereof. However, it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention as described hereinabove and asdefined in the appended claims.

What is claimed is: 1. In an electrophotographic reproducing apparatusemploying a rotating xerographic drum having a series of processingstations disposed about it including a drum cleaning station whereinresidual developer material is removed from the drum surface aftertransfer of the developed image to the copy has been completed, theimprovement in the drum cleaning station comprising a supply roll meansfor a web of cleaning material, said supply roll means being rotatablymounted on spring biased swinging arms to bring said web on said supplyroll into contact with said xerographic drum, a pressure rollerresiliently biased toward said xerographic drum, and a takeup rollerdriven at a predetermined rate with respect to said xerographic drum totake up said web, said web being extended from said supply roll meansalong the surface of said drum to said pressure roller and from saidpressure roller to said takeup roller, thereby to effect cleaning ofresidual developer from said drum through the wiping action of saiddrum.

2. An electrophotographic apparatus having an improved drum cleaningstation in accord with claim 1 wherein said pressure roller is biasedtoward said drum to maintain a pressure of between /2 and 1% pounds perlineal inch of pressure roller length.

3. In an electrophotographic reproducing apparatus employing a rotatingxerographic drum having a series of processing stations disposed aboutit including a drum cleaning station wherein residual developer materialis removed from the drum surface after transfer of the developed imageto the copy has been completed, the improvement in the drum cleaningstation comprising a supply roll means for a web of cleaning material,said supply roll means being rotatably mounted on spring biased swingingarms to bring said web on said supply roll into contact with saidxerographic drum, said supply roll means being resiliently biasedagainst said drum by a force of between 4 and 8 ounces, pressure rollerresilient biased toward said xerographic drum, and a takeup rollerdriven at a predetermined rate with respect to said xerographic drum totake up said web, said web being extended from said supply roll meansalong the surface of said drum to said pressure roller and from saidpressure roller to said takeup roller, thereby to effect cleaning ofresidual developer from said drum through the wiping action of saiddrum, the angle between said supply roll means, said drum's rotationalaxis and said pressure roller being between and

1. In an electrophotographic reproducing apparatus employing a rotatingxerographic drum having a series of processing stations disposed aboutit including a drum cleaning station wherein residual developer materialis removed from the drum surface after transfer of the developed imageto the copy has been completed, the improvement in the drum cleaningstation comprising a supply roll means for a web of cleaning material,said supply roll means being rotatably mounted on spring biased swingingarms to bring said web on said supply roll into contact with saidxerographic drum, a pressure roller resiliently biased toward saidxerographic drum, and a takeup roller driven at a predetermined ratewith respect to said xerographic drum to take up said web, said webbeing extended from said supply roll means along the surface of saiddrum to said pressure roller and from said pressure roller to saidtakeup roller, thereby to effect cleaning of residual developer fromsaid drum through the wiping action of said drum.
 2. Anelectrophotographic apparatus having an improved drum cleaning stationin accord with claim 1 wherein said pressure roller is biased towardsaid drum to maintain a preSsure of between 1/2 and 1 1/2 pounds perlineal inch of pressure roller length.
 3. In an electrophotographicreproducing apparatus employing a rotating xerographic drum having aseries of processing stations disposed about it including a drumcleaning station wherein residual developer material is removed from thedrum surface after transfer of the developed image to the copy has beencompleted, the improvement in the drum cleaning station comprising asupply roll means for a web of cleaning material, said supply roll meansbeing rotatably mounted on spring biased swinging arms to bring said webon said supply roll into contact with said xerographic drum, said supplyroll means being resiliently biased against said drum by a force ofbetween 4 and 8 ounces, a pressure roller resiliently biased toward saidxerographic drum, and a takeup roller driven at a predetermined ratewith respect to said xerographic drum to take up said web, said webbeing extended from said supply roll means along the surface of saiddrum to said pressure roller and from said pressure roller to saidtakeup roller, thereby to effect cleaning of residual developer fromsaid drum through the wiping action of said drum, the angle between saidsupply roll means, said drum''s rotational axis and said pressure rollerbeing between 75* and 120* .